The invention relates to a feeding apparatus for feeding and distributing charge material through a feeding opening onto the molten bath surface of a glass melting furnace, having a movable stand which has a charge hopper, a charging system, a pusher with pusher holder and pusher driver for the production of a pushing motion having horizontal and vertical components, and a heat shield substantially covering the feeding opening, in which at least one opening is disposed for the accommodation of the charging system and the pusher holder.
DE-OS No. 26 25 314 and DE-AS No. 29 44 349 have disclosed feeding apparatus for glass melting furnaces, which have no heat shield, but in which the pushers likewise execute a swinging movement.
In the feeding apparatus according to DE-OS No. 26 25 314, the "doghouse" is largely open at the top and above the opening or the surface of the melt there is disposed a two-substance charging apparatus for cullet and finely granular frit material, in which first the cullet is fed in by means of a chute and then the frit material is poured onto the cullet by means of a cellular wheel air lock. The free fall of the charge material raises large amounts of dust inside and out. Dust is a great hazard to the personnel and to the melting apparatus, so that heat exchangers have to be cleaned of dust deposits periodically--a task which takes days. For melting tanks with a U-shaped flame configuration this type of charging is unsuitable. In front of the doghouse there is disposed a tamping apparatus separate from the charging apparatus, by means of which the poured material is tamped into strips by a movement, consisting of horizontal and vertical components, of a pressing member with a stripping blade, forced partially below the surface of the molten glass, and pushed in strips toward the melting zone of the furnace. This, however, entails the disadvantage that the surface of the melt is raised each time. Such an oscillation of the melt surface is, however, a very undesirable manner of operation. The tamping apparatus has a stationary platform on which tracks are fastened for the longitudinal guidance of the arms holding the tamper. Since there is no heat shield, the problem of sealing off a furnace interior from the surroundings and of sealing off heat shield openings through which holding arms pass does not arise in this arrangement.
From DE-AS No. 29 44 349 it is known to shield the furnace interior and the interior of the doghouse from the feeding apparatus and the surroundings, not with a heat shield but with a kind of bipartite and very complicated coupling device. For the feeding, a sloping plate is provided which is of virtually the same width as the doghose and whose front end extending into the doghouse serves simultaneously as a pusher for the charge material. Such apparatus are also known as chute feeding machines. The pusher is moved along a parallelogram whose longest sides, however, are not parallel to the melt surface but approximately parallel to the feeding plate. The pusher can dip into the melt, therefore, only at the end of the stroke, so that no appreciable stirring action is performed in the melt. Furthermore, a chute feeding machine of this kind produces on the melt surface an undesirable, uninterrupted "carpet" of charge material. The sealing of the very wide feeding plate is, however, difficult and calls for heat-resistant woven parts of large area above the feeding plate, and likewise a heat-resistant, folding fabric apron below the feeding plate. To provide the necessary flexibility this apron has to be thin, but then it can be effective only against dust, but not against the escape of energy. The feeding plate and pusher component, however, has still another serious disadvantage in regard to the degrees of freedom of movement of the pusher: since the charge material is bulk material resting on the feeding plate under the bulk tower, any lifting of the feeding plate parallel to itself would involve a lifting of all of the bulk material. Consequently, by means of a pivoting frame the feeding plate performs a swinging movement with respect to the stationary supporting frame (platform), and it is expressly stated that the pivot axis of the said frame is to be virtually coincident with a line that lies in the area of a so-called sand seal at the bottom end of the discharge opening of the bulk tower. Therefore there is no parallel displacement of the plane of movement of the pusher.
In feeding apparatus of this kind it is important to place the charge material--a mixture as a rule--in a uniform and controllable stream onto the bath surface and distribute it thereon so that the charge material will come as quickly as possible into intimate interaction with the molten glass for the purpose of melting.
DE-GM No. 83 04 858 discloses a feeding apparatus of the kind described above, in which a heat shield is disposed between the pusher and the stand, by which the end of the charging device, a vibratory conveyor trough, extends into the glass melting furnace. More precisely, the end of the charging system enters into the so-called doghouse of the melting furnace. The heat shield serves in this case to solve the problem of reducing the action of radiant heat on the feeding apparatus, especially on its charging device, and at the same time of reducing heat losses as well as the escape of gas and dust from the furnace chamber above the molten glass surface. However, to prevent interference between the heat shield and the pusher holder, a sufficiently large opening has to be provided in the heat shield, which, however, impairs the action of the heat shield.
In the known system, a crank-type vibrating driver engaging the pusher holder sets the pusher into periodical movements in which the bottom edge of the pusher or pusher blade describes a shallow ellipsoid pattern of movement. The crank of the driver motor engages a rod which is fastened fixedly to the pusher holder in the vertical direction. The oscillating shaft of the pusher and pusher holder is mounted on the end of a rocker arm and consequently performs oscillating movements on an arc in which the center of these movements is in the front area of the stand, but not in the area of the opening in the heat shield, so that the latter opening must be of correspondingly large dimensions. On account of the complexity of the pusher movement, no reliably working sealing means can be provided at the point where the pusher passes through the heat shield, so that the effect of the heat shield is limited.
Mainly, however, in the known system the bottom edge of the pusher or pusher blade does not move precisely parallel to the bath surface on account of the above-described elliptical motion, so that the action of the pusher on the charge material floating on the melt surface is different according to the distance between the pusher and the end of the charging system. The charge material must, as it is known, be divided on the melt surface, by the action of the pusher, into individual "pads" of material pushing or pushed on the surface of the melt, so that the molten glass already present will act with as little hindrance as possible on all parts of the charge material.